The presence of a chemical or biological substance has traditionally been detected by utilizing one or more chemical reactions. These chemical reactions are usually irreversible, i. e. the reactions are not reset if the chemical or biological substance is removed from the device. Detection devices that utilize irreversible chemical reactions are typically time consuming and/or expensive to maintain because at least a portion of the detection device needs to be replaced or steps need to be undertaken to reset the device if a quantity of the chemical or biological substance has been detected.
Alternatively, a detection device may be reversible, i.e. the device can be reset automatically if a detected chemical or biological substance is removed. Thus, a reversible device is usually reusable. One type of reversible detection device uses a physics-based, spectroscopic solution to determine the presence of a substance without a chemical reaction. Specifically, light is passed through a waveguide. The light extends into the environment and is reactive to at least one contaminant particle in an adjacent environment. A detector is used to determine the specific contaminant particle and its concentration in the environment based the characteristics of the received light.
An example reversible device uses ultra-thin nanowire fibers as waveguides. The nanowire fiber is thin enough to allow a portion of a lightwave to propagate in, and thereby interact with, the environment adjacent to the nanowire. However, the use of nanowire fiber is limited because nanowire is typically very fragile. It is also difficult to form nanowire coils having orientations other than a straight path due, in part, to the nanowire manufacturing process. These limitations influence the type of platform capable of housing a device and the structures that can be utilized. These limitations are compounded in a chemical or biological sensing device because the nanowire fiber needs to be exposed to the surrounding environment in order to interact with the substance to be detected. In such a platform, it is difficult to ensure only light and substance interactions, without interference from its packaging environment since it needs to be supported. Thus, the supporting environment severely compromises the measurement. Moreover, it is desirable to increase the length of the nanowire fiber used in a sensor because increasing pathlength increases measurement sensitivity. However, increasing the length of the nanowire leads to a device that is even more fragile.